Marfan syndrome (MFS) is an autosomal dominant disorder caused by mutations of the fibrillin locus on chromosome 15. This connective protein defect results in multisystem laxity of the extracellular microfibrillar matrix. The clinical phenotype is heterogeneous and includes age-specific cardiovascular, ocular, musculoskeletal, dermatologic, and pulmonary symptoms. Most children with MFS have valvular disease at the time of diagnoses and most will develop progressive aortic root dilatation, which may lead to aortic dissection and rupture. Preliminary data from the adult MFS literature suggests that 57% of MFS patients will have obstructive sleep apnea syndrome (OSAS). Furthermore, two case reports have documented the association between treatment of OSAS and the stabilization of aortic root dilatation. We hypothesize that the physiological changes induced by OSAS, including hypertension and large intrapleural pressure swings, could be important in the pathophysiology of MFS sequelae in children. To date, no studies have evaluated pre-adolescent MFS children for sleep-disordered breathing. Therefore, our protocol entails evaluating an unselected population of children with MFS for sleep-disordered breathing using overnight polysomnography. Therapy of sleep-disordered breathing in affected MFS children could improve their quality of life and reduce cardiovascular morbidity.